As security is stepped up ahead of Prince Charles’s historic trip to Ireland, concerns have been raised that Irish Islamic extremists may try to target the visit.

In addition to the risk posed by dissident republicans, Gardai are believed to be monitoring a number of radicalised individuals who they fear may attempt to disrupt the poignant trip next week.

Among suspects thought to be under surveillance is Irish man Khalid Kelly, who was arrested, but released without charge, for alleged death threats against Barack Obama when the US president visited Ireland in 2011.

Converting to Islam in 2000 while imprisoned in Saudi Arabia, the 48-year-old is thought to have recently worked as a nurse in Syria before returning to Ireland.

The Irish Mail on Sunday reports that Mr Kelly knew Michael Adebolajo, the man who brutally killed British soldier Lee Rigby by knocking him down with his car before butchering him with a meat cleaver.

Pictured alongside Mr Adebolajo at a demonstration in London in 2007, the 48-year-old told the Irish Mail on Sunday that: “I’ve seen that picture. I kind of knew him at the time of being around, I wasn’t really with him.”

“Everyone was a bit shocked, not by him killing a British soldier, but by the way [he did it] and then doing an interview afterwards.”

“I think that was more shocking than the Charlie Hedbo killing… I think everyone was like ‘no, there’s something not right’.”

In 2011, Khalid Kelly, born Terrence Edward Kelly in 1966, said he would have been happy if President Obama had been killed during his visit to Ireland.

“How could I now feel happy when a big enemy of Islam is gone?” he told the Irish Mirror at the time.

Speaking to the newspaper at a mosque in Cavan, Mr Kelly, who recently changed his name, expressed his belief that Gardai were monitoring him ahead of Prince Charles’s visit.

“I am being monitored all the time. They are not sitting outside, but they are monitoring,” he said.

Asked about visiting Syria, he said “I grew up believing if someone is in trouble, you go and help them.”

“Born in Ireland, you were raised on stories of defending our own way of life, so why don’t Muslims have the same right to do it?”